This invention relates generally to optical crossbar switches and more particularly to reconfigurable monolithic optical crossbar switches capable of amplifying or attenuating the switched signals.
In numerous applications, such as high computation rate parallel or distributed computing architectures with numerous processors which transmit information to each other or share common resources, communication switching systems as in telephone switching centers, and aircraft fiber optic buses that require reconfigurability to allow for redundancy for fault tolerance as well as the ability to share several sensors with each of several processors it is desirable to utilize a reconfigurable interconnection network. One such type of reconfigurable interconnection network is a reconfigurable crossbar switch which is in effect an N.times.M array of switches for connecting each of N inputs for any or all of M outputs.
Initially, electrical crossbar switches were developed and utilized, however, the use of such electrical switches severely limits the bandwidth of the signals transmitted through the switch as well as being quite sensitive to electromagnetic interference (EMI). Additionally, electrical crossbar switches generate EMI themselves. With the advances of speed and volume in data communications, the limitations imposed by electrical crossbar switches have proven to be too constraining and reconfigurable interconnection networks including optical switches or hybrid electrooptical switches have been developed.
Optical or hybrid electrooptical crossbar switches have significantly improved the transmission bandwidth in comparison with electrical crossbar switches as well as reducing the effects of EMI on the switch. Several methods have been utilized in attempts to design optical interconnection networks. One such design involves the electrical detection of an optical signal followed by relaying the transduced electrical signal to the appropriate channel and regeneration of the optical signal at the appropriate output optical channel. Such a process, however, is prone to the introduction of errors during conversion as well as during the relaying processes. Additionally, bandwidth is still limited to the bandwidth of the device electronics and transmission via an electrical signal path can take place in only one direction as opposed to bidirectional optical transmission.
An alternative optical interconnection network is a passive optical transmission path crossbar switches in which an input optical signal is made available to N output ports with the particular output port subsequently selected. Such an optical interconnection network, however, suffers from several deficiencies. In addition to the typically massive size of such systems, the signal in such a device is reduced in strength by a factor of N due to the splitting of the signal in order to make it available to each of the N output ports.
Yet another approach to developing an optical interconnection network is illustrated by the networks disclosed in U.S. Pat. No. 5,037,173 issued on Aug. 6, 1991. In the optical interconnection network discussed in the 5,037,173 patent bifurcated optical fibers with a common end for both emitting light and receiving light are positioned such that light may be emitted from the fibers toward a spatial light modulator which reflects the input light to the desired fiber through which it is to be output. Additionally, the patent discloses the use of a deformable mirror device for reflecting the input light to the desired output fiber. While the optical interconnection network disclosed by the 5,037,173 patent may allow transmission of signals having a wide bandwidth while not being impeded by EMI, such an optical interconnection network must be aligned precisely in order to operate properly and may prove difficult to fabricate.
It would be desirable therefore, for an optical interconnection network to be designed that can provide a high level of signal splitting without signal corruption or loss in bandwidth. Furthermore, it would be desirable for such an optical interconnection network to be bi-directional and to be capable of being fabricated by conventional integrated circuit fabrication techniques with a high level of crossbar function integration on a single monolithic chip. It would also be desirable for the optical interconnection network to be easily reconfigurable to assure system architectural flexibility and fault tolerance.